1. Field of the Invention
The present invention relates to an image forming apparatus to which a sheet processing apparatus that performs post processing on each sheet having an image formed thereon can be connected.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 2002-226121 discloses a structure that lifts up the center portion of each sheet to be discharged from a printer, and has a pair of discharge rollers with rotational members alternately arranged in the rotational axis direction, so as to increase the sheet stackability. This document also discloses a structure that has convex portions forming such a wave-like portion that each sheet cannot easily be folded in the sheet conveying direction. With this structure, each sheet is discharged onto a stacking tray, while being given the sheet stiffness.
Staple stackers are known as sheet processing apparatuses for image forming apparatuses such as printers and copying machines. A staple stacker is provided on a side surface on the sheet discharge outlet side of an image forming main body. Such a staple stacker straightens the end portions of sheets supplied one by one through the sheet discharge outlet of the image forming main body, and performs post processing such as stapling on the sheets.
However, when the sheet processing apparatus is connected to the image forming apparatus disclosed in the above document, each sheet discharged from the image forming main body is conveyed to the sheet processing apparatus, with the same stiffness of the sheet as that in the case of being discharged on the stacking tray. Accordingly, each sheet enters the conveying path of the sheet processing apparatus, while being in such an insecure position as to cause high conveyance resistance in the conveying path. As a result, the top ends of the sheets often cause jamming in the conveying path, and reduce the reliability of the image forming apparatus.
Further, so as to convey each sheet in a stable state to the sheet processing apparatus, it is necessary to add a guide member to secure the position of each sheet in the conveying path between the image forming apparatus and the sheet processing apparatus. With such a guide member, however, the sheet processing apparatus becomes larger in size, and the production costs also increase.